1. Field of the Invention
The present invention relates generally to data communication networks, and more specifically to an ATM (asynchronous transfer mode) connectionless data communication network.
2. Description of the Related Art
In an ATM network, a user packet is segmented at the entry point of the network into a plurality of 53-byte cells each having a 5-byte cell header and a 48-byte payload field. According to the ITU-T Recommendation I.363, the cells at the beginning and the end of the packet are designated as BOM (beginning of message) and EOM (end of message) cells, respectively, and those between these cells are designated as COM (continuation of message) cells. At the exit point of the network, the cells are reassembled into a packet for delivery to the destination.
In an ATM connectionless network, the user message is a single-packet message, known as a datagram. The cell header of the cells that comprise a datagram contains a destination address (DA) field into which the destination of the packet is inserted. Japanese Laid-Open Patent Specification Hei 5-260077 discloses an ATM connectionless data communication system. According to this specification, each node of the network has a DA-RDA translation table in which destination addresses are mapped to reduced destination addresses which are compressed versions of the destination addresses. When the cells of a datagram (packet) are routed from one node to the next, the DA field of each cell is used to search the DA-RDA table for a corresponding reduced destination address. The DA field of the cell is updated with this reduced destination address and the cell is routed according to its DA field. However, if a number of packets from different sources are sent to the same destination, the same destination address will be written into the DA field of the cells from these sources. If these cells exist simultaneously on a communication link of the network, the destination is incapable of discriminating the respective sources of the arriving cells and fails to reassemble them into packets according to their sources.
Therefore, the prior art technique cannot apply to ATM connectionless networks where a number of packets are likely to exist simultaneously on a communication link.